The commercially available lubricating oil compositions are produced from a multitude of different natural or synthetic components. To improve the required properties, according to the field of use, further additives are usually added. The base oils often consist of mineral oils, highly refined mineral oils, alkylated mineral oils, poly-alpha-olefins (PAOs), polyalkylene glycols, phosphate esters, silicone oils, diesters and esters of polyhydric alcohols.
The different lubricants, such as motor oil, turbine oil, hydraulic fluid, transmission oil, compressor oil and the like, must satisfy extremely high criteria such as high viscosity index, good lubricant performance, high oxidation stability, good thermal stability or comparable properties.
High-performance lubricant oil formulations which are used as transmission, industrial or motor oils are oils with a special performance profile with regard to shear stability, low-temperature viscosity, long service life, evaporation loss, fuel efficiency, seal compatibility and wear protection. Such oils are currently being formulated preferentially with PAO (especially PAO 6) or group I, II or Group III mineral oils as carrier fluids, and with specific polymers (polyisobutylenes=PIBs, olefin copolymers=ethylene/propylene copolymers=OCPs, polyalkyl methacrylates=PMAs) as thickeners or viscosity index improvers in addition to the customary additive components. Together with PAOs, low-viscosity esters are typically being used, for example DIDA (diisodecyl adipate), DITA (diisotridecyl adipate) or TMTC (trimethylolpropane caprylate), especially as solubilizers for polar additive types and for optimizing seal compatibilities.
Esters are used as co-solvent, especially in motor oil, turbine oil, hydraulic fluid, transmission oil, compressor oil, but esters are also used as base oils, in which they are the main component.
EP 0 767 236 A1 discloses a gear lubricating oil composition. The composition contains more than 20% by volume a hydrogenated polyalphaolefin, and less than 80% by volume of mineral oil or synthetic ester oil or a combination thereof. The examples contain 10% by volume bis(tridecyl)-adipate.
WO 98/04658 A1 discloses base stocks for synthetic gear oils for use in heavy and medium duty axle gear lubricants and transmission fluid application. The lubricant disclosed therein contains 1% to 20% by weight of an ester. The ester includes diesters of C8-13 adipates, in particular diisodecyl adipate.
U.S. Pat. No. 4,370,247 discloses a gear or axle lubricant containing 25 to 60 mass % of at least one di-C8-12 alkyl ester of a dicarboxylic acid. The whole lubricant disclosed therein is reported to decrease power loss due to friction, therefore conserving fuel consumption.
CA 2 637 401 discloses a variety of diesters derived from a dicarboxylic acid having 2 to 36 carbon atoms and a branched alcohol having 4 to 40 carbon atoms. The lubricants can contain 0.1 to 100% by weight, or 5 to 99% by weight of the diesters.
WO 2011/34829 A1 discloses a method of lubricating a limited slip differential comprising supplying to the limited slip differential a lubricating composition comprising C4-30 diester of adipic acid.
Although different lubricants, such as motor oil, turbine oil, hydraulic fluid, transmission oil, compressor oil and the like, satisfy extremely high criteria such as high viscosity index, good lubricant performance, high oxidation stability and good thermal stability, there is still a need to reduce the amount of energy consumed in operation of mechanical devices.